I would have thought "elope to (destination for the marriage)" was correct. However, I recently saw someone write "elope in (destination for the marriage)," and when I looked it up, the answer wasn't clear as Google Ngrams shows both are used, while Merriam-Webster dictionary only gives examples with "elope in".
Here's how I think they should be used:
"They eloped in New York" = "They were in New York, and they went
away from their families and got married in New York."
"They eloped to New York" = "They were in another city, and they went away from their families to the city of New York, where they got married."
What do you think?